Can You Ever Fit and Forget Surface Water Drainage?

Is there ever a time when a drainage system can be left unmaintained? And how does an owner or operator really know if it is performing as the designer intended?

These are really not trick questions: clearly a piped system or a manufactured device will have a schedule for servicing that, if followed, will ensure that it performs as intended throughout its life. But what if the drainage component is an above-ground ‘natural’ feature such as a pond or wetland, a detention basin or a filter strip?

Without knowing for sure exactly how Sustainable Drainage Systems (SuDS) will perform and operate throughout their life, how can any organisation take over responsibility for them with confidence? Charges and legal contracts agreed between the developer and the organisation that adopts and/or maintains them, require maintenance tasks to be clear and predictable to avoid disputes. Whether you are a private site management company, a water company or local authority, you need to be able to predict maintenance costs and understand the type and frequency of tasks to be carried out.

Of course, this is by no means a new problem. The Engineering Nature’s Way SuDS in Scotland survey demonstrated some of the challenges that can occur when systems are left ‘in limbo’ due to organisational differences over the adoption and maintenance of SuDS systems.

Regulations

In England, new legislation was proposed to solve the problem by making local authorities responsible for adopting and maintaining all SuDS in new developments. But that idea was scrapped. Alternative regulations are now in place that expect local planning authorities only to grant developers planning permission if they set out a clear maintenance schedule for the lifetime of the development, with an acknowledgement that this needs to be ‘economically proportionate’ if the SuDS are to be viable.

However, there has been concern that the English regulations lack clarity and allow developers and local planning authorities leeway to ignore the need for SuDS, especially if a SuDS solution can be argued to make a development commercial unviable.

Maintenance Overlooked?

In our excitement to see the delivery of imaginative SuDS designs considered as a routine element of new development, the importance of maintenance has been overlooked. As a result, there is likely still to be reluctance among water companies and local authorities to adopt SuDS. And with the developer responsible for making provisions, there could still be conflicts and delays. For example, a recent homes development in Winchester was reported to be facing difficulties after local authority management of SuDS was rejected, leaving residents concerned about unspecified maintenance costs for years to come.

So what is the answer? We need to begin with an understanding that all drainage systems are precision engineered. Whatever the choice of components used to build the management train they must meet exact performance criteria such as the rate of infiltration, discharge into a watercourse, the volume of flood storage, the pollutants to be removed and so on.

As precision-engineered systems they must be monitored and measured regularly, they must continue to be maintained according to the intentions of the designer, and there must also be a clear understanding of what the design lifetime of the component is.

Pragmatic Ways Forward

So what can a developer or their consulting engineer do in practical terms today to ensure that maintenance issues don’t become a barrier to a sustainable scheme – or to getting it adopted or maintained appropriately?

A combined approach using both natural and manufactured elements is one particularly effective answer. Manufactured devices provide the scientific evidence of surface water control and/or pollutant removal that can satisfy the authorities. Working with a manufacturer’s specialist design team such as Hydro International’s can help in putting together a robust engineered solution that has clearly laid out maintenance schedules to follow.

It should be always be an enforceable requirement of the local planning authority to check that SuDS are constructed and continue to operate as designed, against clear, scientific criteria. For the future, industry and academia must continue to develop data and evidence on the performance of all SuDS components to enable accurate through-life operational costs to be predicted.